The conventional MRI (Magnetic Resonance Imaging) RF (Radio Frequency) coil or a birdcage resonator known from MRI instrumentation cannot be used in the frequency band 100-500 kHz since its quality factor Q, the “gain” of the resonator, becomes very low (less than one). As a result, the induced electric field in a body will be low too. To achieve high levels of the stimulation electric field, a birdcage coil resonator operating at a much lower carrier frequency of around 100-500 kHz is required. The carrier may then amplitude-modulated by any required base frequency in the range of 0-1000 Hz or by constructing pulsed excitation with a center frequency not to exceed 1000 Hz.
Accordingly, a resonator with a high field, up to 1-2 volts per centimeter, that operates at much lower than frequencies is required. The birdcage resonator of the present invention uses a very large number of rungs in excess of 100 while the conventional MRI resonator uses 8-16 rungs. It also uses inductively coupled feeds. These two factors allow achievement of a very high quality factor of 300 and high-fields of 1-2 volts per centimeter. Such a device may be used to modulate the field level with any signal including electroencephalographic signals from the brain to establish closed-loop feedback for the entire peripheral and/or nervous system. Other potential applications include treatment of chronic pain, oncological and psychiatric applications.